kernel: timeout: add syscall for runtime clk freq

If the system sets its clock frequency at runtime, this is
stored in a variable that can't be directly read by user
mode. For this case only, add a system call to fetch its
value and modify the definition of
sys_clock_hw_cycles_per_sec() to use it.

Since this is now a system call, store in a temporary variable
inside z_ms_to_ticks(). The syscall overhead only applies
when called from user mode, other contexts are completely
inlined.

Added stub syscall header for mocking framework, to get rid
of inclusion errors.

Fixes: #16238

Signed-off-by: Andrew Boie <[email protected]>

Author: Andrew Boie

include/sys_clock.h

@@ -31,12 +31,21 @@ extern int _sys_clock_always_on;
 extern void z_enable_sys_clock(void);
 #endif
 
-static inline int sys_clock_hw_cycles_per_sec(void)
-{
 #if defined(CONFIG_TIMER_READS_ITS_FREQUENCY_AT_RUNTIME)
+__syscall int z_clock_hw_cycles_per_sec_runtime_get(void);
+
+static inline int z_impl_z_clock_hw_cycles_per_sec_runtime_get(void)
+{
 	extern int z_clock_hw_cycles_per_sec;
 
 	return z_clock_hw_cycles_per_sec;
+}
+#endif /* CONFIG_TIMER_READS_ITS_FREQUENCY_AT_RUNTIME */
+
+static inline int sys_clock_hw_cycles_per_sec(void)
+{
+#if defined(CONFIG_TIMER_READS_ITS_FREQUENCY_AT_RUNTIME)
+	return z_clock_hw_cycles_per_sec_runtime_get();
 #else
 	return CONFIG_SYS_CLOCK_HW_CYCLES_PER_SEC;
 #endif
@@ -100,11 +109,11 @@ static ALWAYS_INLINE s32_t z_ms_to_ticks(s32_t ms)
 #ifdef CONFIG_SYS_CLOCK_EXISTS
 
 #ifdef _NEED_PRECISE_TICK_MS_CONVERSION
+	int cyc = sys_clock_hw_cycles_per_sec();
+
 	/* use 64-bit math to keep precision */
-	return (s32_t)ceiling_fraction(
-		(s64_t)ms * sys_clock_hw_cycles_per_sec(),
-		((s64_t)MSEC_PER_SEC * sys_clock_hw_cycles_per_sec()) /
-		CONFIG_SYS_CLOCK_TICKS_PER_SEC);
+	return (s32_t)ceiling_fraction((s64_t)ms * cyc,
+		((s64_t)MSEC_PER_SEC * cyc) / CONFIG_SYS_CLOCK_TICKS_PER_SEC);
 #else
 	/* simple division keeps precision */
 	s32_t ms_per_tick = MSEC_PER_SEC / CONFIG_SYS_CLOCK_TICKS_PER_SEC;
@@ -234,4 +243,6 @@ struct _timeout {
 }
 #endif
 
+#include <syscalls/sys_clock.h>
+
 #endif /* ZEPHYR_INCLUDE_SYS_CLOCK_H_ */

kernel/timeout.c

@@ -28,7 +28,14 @@ static int announce_remaining;
 
 #if defined(CONFIG_TIMER_READS_ITS_FREQUENCY_AT_RUNTIME)
 int z_clock_hw_cycles_per_sec = CONFIG_SYS_CLOCK_HW_CYCLES_PER_SEC;
-#endif
+
+#ifdef CONFIG_USERSPACE
+Z_SYSCALL_HANDLER(z_clock_hw_cycles_per_sec_runtime_get)
+{
+	return z_impl_z_clock_hw_cycles_per_sec_runtime_get();
+}
+#endif /* CONFIG_USERSPACE */
+#endif /* CONFIG_TIMER_READS_ITS_FREQUENCY_AT_RUNTIME */
 
 static struct _timeout *first(void)
 {

subsys/testsuite/ztest/include/syscalls/sys_clock.h

@@ -0,0 +1,3 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ */